I would agree that aluminum heads are a must. My '95 R started out life with iron GT40 heads. The aluminum GT40 heads did not come out in time to make it into this car. When I built my 408 stroker I used GT40X heads which were the best aluminum heads Ford had at the time. When I built my current 429 stroker I bought a set of Brodix Track1 CNC ported by M2 Race Systems to Tom Slawko port designs. These are pretty good heads, but there are better now. I was playing it conservative setting up for only 9.75:1 compression. These Brodix heads have large 76cc chambers and I still needed to use a 13cc dish piston. Make sure you do your compression ratio calculations to achieve your goal. Include the compressed head gasket volume, area above the top ring, everything.
I will be going through my engine again this year, mostly due to the fact that the machinist who honed my aluminum block did not do so correctly and, consequently, my rings never seated. I'm upgrading from the Brodix to TrickFlow CNC R-Series 225 heads with 64cc CC to give me 11.0:1 compression and around 10% better flow. I'm also upgrading the cam to a CompCams 4-pattern 35-563-44 cam and 15931-16 short-travel lifters. I'm hoping that having higher compression, rings that actually SEAL, heads that breath considerably better and a significantly hotter cam will allow me to achieve between 650 and 700hp with no power adders.